An Etymological Dictionary of Astronomy and Astrophysics
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Math.: A number which scales, or multiplies, some quantity. In the equation y = Cx, C is the scale factor for x. C is also the coefficient of x, and may be called the constant of proportionality of y to x.
Geometry: The ratio of any two corresponding lengths in two similar geometric figures. The ratio of areas of two similar figures is the square of the scale factor.

→ scale; → factor.

An agreement by competent observers of a series of observations of the same phenomena. From time to time scientific facts are revised by additional data (G. Smooth, Lawrence Berkeley Lab website).

→ scientific; → fact.

The → Coulomb interaction reduced owing to the presence of other electrons. See → shielding effect.

→ screen; → coulomb; → interaction.

The beginning of the total phase of a solar eclipse when the leading edge of the Moon touches the eastern edge of the Sun completely obscuring the Sun.

→ second; → contact.

A fraction in which the → numerator and → denominator are positive → integer numbers. Compare → compound fraction.

→ simple; → fraction.

The act or instance of removing the contribution of non-related, intervening foreground light to the object.

→ sky; → subtraction.

The general term for all forms of short-lived phenomena on the Sun, including → solar flares, → sunspots, → prominences, etc., indicating that the Sun is an active star.

→ solar; → activity.

Same as the → solar cycle.

→ solar activity; → cycle.

For the translational motion of a spherical body moving in a → viscous fluid, the proportionality factor between the uniform flow velocity far from the sphere and the drag force, provided no-slip boundary condition and small → Reynolds numbers: f = 6πηR, where η is the Reynolds number and R radius of the sphere.

→ Stokes; → friction; → factor.

The interaction between quarks that is transmitted by gluons. The characteristic range of the strong interaction is 10^-13 cm, and the time scale over which it operates is on the order of 10^-23 second. Also called → strong force.

→ strong; → interaction.

A → nuclear reactor in which the rate of production of → fission neutrons is lower than the rate of production in the previous generation, and therefore the number of fissions decreases over time.

→ subcritical; → reactor.

To take one number away from another; deduct. To perform the arithmetic operation of → subtraction.

From L. subtractus, p.p. of subtrahere "to draw from beneath, take away, draw off," from → sub- "from under" + trahere "to pull, draw."

Zirkaršidan, literally "to draw beneath," from zir-, → sub-, + karšidan "to draw, pul, drag," variant of kašidan "to draw, protract, trail, drag, carry;" Av. karš- "to draw; to plow," karša- "furrow;" Proto-Iranian *kerš-/*xrah- "to draw, plow;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base k^wels- "to plow."
Kâhidan, → decrease.

The operation of finding the difference between two numbers or quantities.

Verbal noun of → subtract.

1) Constituting or involving → subtraction.
2) Math.: Indicating or requiring subtraction; having a → minus sign.

→ subtract; → -ive.

Color produced by mixing pigments rather than light. Mixing all of the subtractive colors together results in the color black. See also → additive color.

→ subtractive; → color.

Of or pertaining to a system composed of nearby groups and clusters of galaxies in the → local Universe. Se also → galaxy cluster.

→ super-; → galactic.

A spherical → coordinate system in which the → equator is the → supergalactic plane. Supergalactic longitude, SGL, is measured → counterclockwise from direction l = 137.37 deg, b = 0 deg (between 0 and 360 deg). The zero point for supergalactic longitude is defined by the intersection of this plane with the → Galactic plane. In the → equatorial coordinate system (J2000) this is approximately 2.82 h, +59.5 deg. Supergalactic latitude, SGB, is measured from the supergalactic plane, positive northward and negative southward. The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates l = 47.37 deg, b = +6.32 degrees, corresponding to the equatorial coordinate system (J2000) 18.9 h, +15.7 deg.

→ supergalactic; → coordinate; → system.

→ supergalactic coordinate system.

→ supergalactic; → latitude.

→ supergalactic coordinate system.

→ supergalactic; → longitude.

The symmetry plane of the → Local Supercluster, where density of galaxies in our environment is the largest. The plane passes through the → Virgo cluster of galaxies, about which many of the brightest galaxies in the sky are concentrated. The supergalactic plane was recognized by Gérard de Vaucouleurs (1918-1995) in 1953 from the  → Shapley-Ames catalogue.

→ supergalactic; → plane.